Image display devices such as liquid crystal displays, organic electroluminescent displays, and plasma displays provide high-definition image quality with low power consumption. Such image display devices are also slim due to the flat screens thereof. These image display devices are being used not only in offices or households but also at sites of various kinds of professional work, such as graphic design and medical care.
Various efforts have been made to increase the reproducibility of display images produced by liquid crystal image display devices, including the control of the luminance of a backlight in an image display unit by measuring light from the backlight.
Patent Literature 1 discloses a configuration in which an illumination element is exposed by cutting off one edge of light guide means (diffusion plate) in a backlight and in which a light receiving element is exposed by cutting off the other edge of the diffusion plate (see Claims or FIG. 1(B) thereof). In Patent Literature 1, the light receiving element receives light from the backlight as well as light from the outside of the device to reduce the power consumption of the backlight, without distinguishing between the outside light and backlight light.
Patent Literature 2 discloses a configuration in which light from an LED light source in an LED box in a backlight is received by an optical sensor through a light guide (optical fiber) (see paragraph [0028] or FIG. 14 thereof). In Patent Literature 2, the sensor or optical fiber is disposed near the LED and therefore the LED box has to be drilled.
Patent Literature 3 discloses a configuration in which an optical sensor is exposed by obliquely cutting off one edge of a light guide plate in a backlight (see paragraph [0032] or FIG. 4(a) thereof).
Patent Literature 4 discloses a configuration in which a light-shielding member is in contact with one edge of a light guide plate in a backlight and in which light from a pinhole formed in the light-shielding member is received by an optical sensor (see paragraph [0020] or FIG. 1(a) thereof).
Patent Literature 5 discloses a configuration which is provided with an inclined surface for reflecting light from an exposed surface of a side surface of a light guide plate in a backlight toward the back surface thereof and in which the light from the inclined surface is received by an optical sensor (see Claim 2 or FIG. 1 thereof).
Patent Literature 6 discloses a configuration in which a gap is formed in a predetermined position of an area in which the wall surface and bottom surface of a backlight case are connected together and in which a light receiving element is disposed in this position (see paragraph [0057] of FIG. 14 thereof).
Patent Literature 7 discloses a configuration in which a notch is formed at the bottom of an end surface of a light guide plate in a backlight and in which a photodetector is housed in the notch (see paragraph [0029] or FIG. 3(d) thereof).
Patent Literature 8 discloses a backlight unit including at least a frame-shaped chassis, a light guide plate disposed in the chassis, a shield plate disposed at least on the back surface of the light guide plate, a light source disposed on one end surface of the light guide plate, and light detection means disposed on the other end surface of the light guide plate and configured to detect light leaking from the other end surface. In this backlight unit, the shield plate and light detection means are fastened to each other using a screw; the chassis, shield plate, and light guide plate are fastened to each other using screws; and the distance between the other end surface of the light guide plate and the light detection means is kept approximately constant (see Claim 2 or FIG. 1 thereof).
Patent Literature 9 discloses a configuration in which a light guide tube is provided by drilling a backlight module and in which part of light entering a side wall of a rear plate is detected by a detection unit disposed on a soft circuit substrate (see paragraph [0015] or FIG. 4 thereof).